.22 Winchester Short Magnum
.22 WMR (left) compared to .22 ILARCO (right)
Type	Rifle
Place of origin	United States
Production history
Designed	1987[1]
Manufacturer	Winchester
Specifications
Parent case	.22 WMR
Case type	Rimmed, straight
Bullet diameter	.224 in (5.7 mm)
Neck diameter	.242 in (6.1 mm)
Base diameter	.242 in (6.1 mm)
Rim diameter	.294 in (7.5 mm)
Rim thickness	.050 in (1.3 mm)
Case length	.669 in (17.0 mm)
Overall length	.950 in (24.1 mm)
Primer type	Rimfire
Ballistic performance
Bullet mass/type Velocity Energy 40 gr (3 g) FMJ 1,350 ft/s (410 m/s) 160 ft⋅lbf (220 J)

The .22 ILARCO / 5.7x24mmRF, also known as the .22 Winchester Short Magnum Rimfire or .22 American,^[2][3] was a rimfire cartridge designed in 1987 for the American-180 rimfire submachine gun. At the time the cartridge was created, the design of the American-180 had been taken over by the Illinois Arms Company, Inc., hence the ILARCO name.

Sometime after the Illinois Arms Company, Inc. (ILARCO) purchased the rights to the American-180 they determined a more powerful cartridge would be appropriate, which resulted in the creation of the .22 ILARCO. The new cartridge was designed so that a simple change of barrel was all that was required to switch between standard .22 Long Rifle, for which the gun was designed, and the new cartridge.

The .22 ILARCO uses a shorter version of the .22 Winchester Magnum Rimfire case, which use the same 40 gr (2.6 g) projectile as the original .22 Winchester Magnum Rimfire cartridge.

• 5 mm caliber
• List of rimfire cartridges